M33 is a nearby example of a spiral galaxy. It is only slightly inclined
to our line of sight such that we can see both structure in the spiral
arms, and the central bulge. Observations of galaxies like these can help
us determine the structure of our own Galaxy, the Milky Way.

This image shows M33 in infra-red light (at a wavelength of 60 microns)
from the Infrared
Space Observatory (ISO). As well as tracing populations of cooler
stars, photons in this part of the spectrum trace the warm dust found in
regions where new stars are forming. The young stars illuminate the
surrounding gas which absorbs he light and re-radiates it in the
infra-red.